Various systems and techniques are known for tracking the location of objects. These involve the use of bar-codes and other optically sensible codes.
The following U.S. patents and Published PCT Applications are believed to represent the current state of the art:
U.S. Pat. Nos. 6,460,769; 6,456,239; 6,445,810; 6,442,476; 6,433,732; 6,427,913; 6,424,260; 6,405,924; 6,400,830; 6,384,409; 6,381,509; 6,339,745; 6,317,044; 6,286,763; 6,265,977; 6,285,342; 6,283,375; 6,259,408; 6,252,508; 6,206,286; 6,127,928; 6,070,801; 6,098,877; 6,027,022; 5,996,895; 5,988,508; 5,912,980; 5,828,049; 5,828,048; 5,825,012; 5,646,389; 5,621,864; 5,600,121; 5,528,228; 5,468,949; 5,384,859; 5,224,373; 4,924,799; 4,844,509; 4,794,238; 4,636,950; 4,340,810; 4,340,008; 4,268,179; 4,044,227 and 3,961,323.
Published PCT Applications WO 00/04711 and WO 98/10358.
The disclosures of the foregoing U.S. patents and Published PCT Applications are hereby incorporated by reference.